Generally, OPC (One Point Copy) is known as one of methods for backing up a copy source volume, for example, an operation volume, in a storage product or a computer. The OPC is a function for producing a snapshot which is data at a predetermined point of time regarding data which is a backup target. If an OPC instruction is received from a user, then a backup apparatus which executes the OPC copies all data of operation volumes at a point of time at which the OPC instruction is received to store the data as a snapshot (backup data) to carry out backup of the operation volumes.
As an expansion function of the OPC described above, QOPC (Quick One Point Copy) in which a background copy method is used as a function for implementing difference copy, SnapOPC+ (Snapshot One Point Copy+) in which a copy on-write method is used as a function for implementing copy of a plurality of generations and so forth are available.
The QOPC and the SnapOPC+ are described below.
The QOPC is a function for producing a backup volume of an operation volume at a certain point of time similarly to the OPC. With the QOPC, an operation volume and a backup volume can be referred to and updated instantaneously as if production of the backup volume were completed at the same time with a response to a QOPC starting instruction.
In the QOPC, a copying process operates in the background after the QOPC starting instruction is completed. However, if a request for reference to and updating of a region of a backup volume in which background copy is not completed is issued, then the reference and updating are carried out after the copying process for the relevant region is carried out. Further, in the QOPC, different from the OPC, an updated portion from that at a point of time at which a backup is acquired in the immediately preceding cycle is stored after the background copy is completed. Therefore, in the QOPC, production of backup volumes for the second time and so forth can be carried out merely if only difference data is copied in the background.
The SnapOPC+ is a function for implementing copy of an operation volume without carrying out allocation of a capacity same as that of the operation volume as a region of a backup volume. By such a function as just described, reduction of a disk capacity necessary for backup can be implemented in a user environment wherein it is expected that the entire volume is not updated and the cost required for the copying can be decreased. In the SnapOPC+, it is assumed that it is used mainly for volume production for tape backup. For the backup volume, a virtual volume having a disk capacity smaller than the capacity of the operation volume is prepared. The virtual volume can be logically accessed from a server similarly to a normal volume.
The SnapOPC+ does not carry out copy of the entire operation volume but is implemented by copying, in the case where an operation volume is updated, data (old data) before updating at an updating target portion into a backup volume which is a copying destination. Where a backup volume which is a copying destination is accessed from a server, if an access target region is not copied as yet, then the server refers to data in a region of the operation volume corresponding to the access target region in place of the access target region. Further, by preparing a plurality of backup volumes, backup volumes of a plurality of generations can be produced.    [Patent Document 1] Japanese Patent Laid-Open NO. 2006-107162    [Patent Document 2] Japanese Patent Laid-Open NO. 2006-048300    [Patent Document 3] Japanese Patent Laid-Open NO. 2007-334709    [Patent Document 4] Japanese Patent Laid-Open NO. 2009-146228
If it is intended to implement backup for a plurality of generations using the advanced copy functions in the present situation described above, that is, the QOPC and the SnapOPC+, then there is such a subject described as below.
If it is intended to apply the QOPC to implement backup for a plurality of generations, then a number of volumes having a capacity same as that of operation volumes equal to the number of generations are required. Therefore, a great amount of disk capacity and a very high cost are required.
Further, in the SnapOPC+, while data before updating in a region in which updating has been carried out in the operation volume is copied into the backup volume, data in a region in which updating has not been carried out is not copied into the backup volume and backup of the data is not carried out. In other words, data in all regions of the operation volume are not copied or backed up into the backup volume which is a copying destination. Therefore, if the operation volume is damaged, then unless updating of data in all regions of the operation volume is carried out and data before updating are copied into the backup volume before the damage, then reference and updating regarding backup volumes of all generations cannot be carried out. Therefore, the data, copied in the backup volume become useless as the backup.